> Ubuntu's low-latency kernel is mostly Kconfig configuration changes applied to their kernel build that they are now at least considering to make by default.
Ubuntu used to have an absolute monster of a hacked up franken-kernel compared to mainstream, but (very fortunately) over the years it's gotten much, much closer to upstream. It was honestly a bit of a nightmare trying to apply a set of custom patches on top of it (to improve a driver that was buggy for many years that I hacked in a way that made it work awesome but would never be accepted upstream because it violated FCC regulations). I'm an outside observer so pure speculation, but I have suspected that it was painful for the Canonical kernel team just as it was for me, and that they made a concerted effort to get away from the craziness. In related news, the people who backport kernel fixes to LTS versions they maintain for their distros (think Canonical and Red Hat, for example) are some of the most unsung heroes in the world. That work is brutal and takes a lot of dedication, and when you're doing your job perfectly nobody knows, but when you mess up everybody knows. That leads to a lot of thanklessness.